Capillary heat transfer device for refrigerating apparatus



.Aug. 31, 1948, R. s. GAUGLER CAPILLARY HEAT TRANSFER DEVICE 'FOR REFRIGERATING APPARATUS Filed April 30, 1945 2 Sheets-Sheet 1 R. S. GAUGLER v(FAPILLARY HEAT TRANSFER DEVICE Aug. 31, 1948.

FOR REFRIGERATING APPARATUS 2 She ets-Sheet 2 FIGS Filed April 30, 1.945-

v 3.8 as

v IMMWMMMM FIG. 4

FIG. 3

- JINiENTOR.

FIG. 2

Patented Aug. 31, 1948 OFFICE A CAPILLARY HEAT TRANSFER DEVICE FOR REFRIGERATING APPARATUS Richard S. Gaugler, Dayton,'0hio, assignor to General Motors Corporation, Dayton, corporation of Delaware Ohio, a

Application April 30, 1945, Serial No. 591,113

My method relates to the art of transferring heat and particularly to a method of and apparatus for transferring heat from one point to another.

In my Patent 2,350,348, I disclosed a secondary heat transfer system capable of transferring heat downwardly a substantial distance. The structure disclosed employed sintered, powdered iron as the capillary material for raising the volatile liquid from the point of condensation up to the point of evaporation.

This sintered iron is formed from a powder and then either sintered inside the tubing, or molded and sintered outside of the tubing after which it inserted into the tubing. Since sintered iron is brittle and cannot be :bent without breaking, this is a considerable limitation and makes it difficult to work with.

It is an object of my invention to provide a secondary heat transferring circuit which is capable of transferring heat downwardly and which can be bent or formed as desired.

It is another objectof my invention to provide a secondary heat transfer circuit capable of transferring heat downwardly which has flexible and durable continuous capillary means which can be readily included in secondary circuits of a variety of configurations.

lit is another object of my invention to provide a more efficient secondary heat transfer circuit capable of transferring heat downwardly more rapidly and particularly one which will transfer heat downwardly a greater distance.

It is still another object of my invention to provide a more efficient capillary means capable of lifting volatile liquid to greater heights.

It is another object of my invention to provide a secondaryheat transfer circuit of the capillary type wherein substantially all the evaporation will take place at the surface of the capillary material and the vapor therefrom can return to the place of condensation without passing through the capillary material.

'It is another object of my invention to provide for a secondary heat transfer circuit of the capillary type a means for efliciently transmitting heat from the walls of the tubing directly to the surface of the capillary material and to provide a path for. the flow of vapors from said surface of the capillary material directly to a place of condensation without forcing the vapors to pass through the capillary material.

The invention in its most elementary form contemplates a secondary heat transfer circuit employing a simple closed piece of metal tubing con- 11 Claims. (Cl. 62-125) taining a volatile liquid and a capillary structure or wick. The capillary structure or wick is formed of glass wool silver or yarn extending lengthwise within the tubing. This silver or yarn is formed of extremely fine discontinuous or staple glass wool fibers averaging 0.00008" in diameter. It is preferably compacted by compression to a density of between about 0.2 and 0.5 g. per cc. and held in that state by enclosing it in a braiding of either continuous or staple glass 'fiber thread. This forms a wick which gives an unusually high capillary lift. This high lift apparently is attributable to the properties of glass and the fineness of the fiber.

To provide unrestricted evaporation of the volatile liquid and the easy return of vapor to the place of condensation as well as good direct heat transfer between every point on the tubing and nearest point on the surface of the wick, the wick is enclosed in a woven or knitted sleeve of fine wire which slightly spaces the wick from the walls of the tubing. The wire sleeve containing the wick is packed tightly within the tubing so that its entire exterior surface presses firmly against the interior surface of the tubing while its interior surface presses tightly against the outer surface of the wick. As the volatile liquid, the tubing preferably contains very pure anhydrous ammonia in an amount sufilcient to saturate the wick and also provide a considerable amount of free liquid at the lower end of the wick sumcient to keep it immersed in the liquid under all conditions wherein operation is desired. Where freezing is not a problem, water may be used as the volatile liquid.

To secure maximum performance. itis necessary to obtain an adequate rate of flow of the liquid ammonia from the pool of free liquid at the bottom of the tube and maximum capillary lift to the place of evaporation. The maximum fiow and maximum lift cannot be attained with the same amount of compacting or density, since the upper limit of compacting or density is necessary to obtain maximum lift while a much lesser amount of compacting or lesser density is required to obtain the maximum fiow of liquid through the capillary material.

Where for manufacturing convenience and economy it is necessary to make the glass wool wicking and the tubing uniform from top to botfrom the bottom to the top either gradually or in two or more steps as in Fig. 4, the density at the bottom of the wick is preferably made low, such as 0.2 g. per cc. to secure larger capillary spaces for maximum flow since only a low lift is required there. The density at thetop is preferably made high, such as 0.5 g. per cc. since high lift and lesser floware needed there for best results. Any intermediate steps are made at intermediate densities increasing progressively from bottom to the top of the wick. However, instead of progressively increasing the amount of glass fiber in the wicking in a tube of uniform size, an increase in density may also be obtained by progressively reducing the size of the tubing and allowing the amount of glass in the wick to remain constant, for example by tapering the tubing as in Fig. 6 or reducing it in steps or merely by progressively flattening it from the bottom to the top. Since normally, evaporation takes place all along the wick, the liquid fiow requirements are greatest at the bottom and decrease gradually from the bottom to the top. Apparently, however, somewhat analogous results have been obtained byusing a combination of fine sliver and slightly larger continuous filaments as in Fig. 5.

With any of these arrangements, the tubing can be bent as desired and the glass wool wick can be inserted before or after the bending of the tubing. The best results which have been obtained thus far are more than twice as good as the best results obtainable with the sintered iron powder capillary disclosed in my Patent No. 2,350,348. -Although for this purpose fine glass fiber and pure anhydrous ammonia have been found definitely superior to any other fibers and volatile liquids, it is possible to use other fibers and volatile liquids where lesser lifts are satisfactory, such as for example steel wool, "Nylon, rayon, animal wool, and cotton, and ethyl and methyl alcohol.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Fig, 1 is a rear sectional view of a refrigerator cabinet taken substantially along the lines l-l of Fig. 2;

Fig. 2 is a sectional view taken substantially along the lines 22 of Fig. 1;

Fig. 3 is a sectional view of the header and one of the tubes taken substantially on the line 3-3 of Fig. 1;

Fi 4 is a view illustrating the arrangement of the strands of glass fiber in the tubes of the secondary system shown in Figs. 1 to 3;

Fig. 5 is a fragmentary view of the tubing showing a modified arrangement of glass strands and glass fibers; and

Fig. 6 is a fragmentary view showing a modifled form of tubing containing glass fiber wicking.

Referring now to the drawings to illustrate one of the applications of my invention, there is shown a refrigerator cabinet 2|] including outer walls 22 surrounding the insulation 24 which encloses the primary evaporator 28 and the boxshaped inner liner member 28. The primary evaporator 25 is made of two sheets of metal spaced apart to provide refrigerant passages therebetween. It encloses the bottom, rearrand sides of the frozen storage compartment 30 located in the bottom of the cabinet 20. The ttom edges of the inner liner member 28 are turned inwardly at an angle of about 45 to form a flange 82 which is separated by a breaker strip of thermal insulating material from an outwardly turned, flange 34 provided around the upper edges of the primary evaporator 28.

" Supported upon the flange 82 is a horizontal partition 36 of some suitable transparent material of low conductivity such as polymethyl methacrylate. The perimeter of this partition 86 is provided with a sealing strip 38 of a rubberlike material providing a seal between it and the door 40 as well as the flange 32 at the bottom of the inner liner 28.

Liquid refrigerant is supplied to the primary evaporator 26 and evaporated refrigerant is withdrawn therefrom through a suction conduit 42 by a condensing unit which includes a sealed motor compressor unit 44, a condenser l6, and a restrictor 48 which controls the flow of liquid refrigerant into the primary evaporator 28. The liquid refrigerant evaporates underreduced pres sure within the primary evaporator to maintain the temperature. below freezing within the storage compartment 30.

To maintain the moist storage compartment 28 cool without dryness, it is necessary to provide a large refrigerated area kept at temperatures only slightly below the temperature to which it is desired to keep the air in the compartment 28. To do this, I employ my improved secondary heat transfer circuit capable of carrying the heat from the top of the inner liner 28 down to the primary evaporator 26, This secondary heat transfer circuit takes the form of a header in into which extends as many small tubes as are necessary to cool a sufficiently large area of the inner liner member 28. In the drawings, eleven tubes are shown with the outermost tubes 52 and 54 extending half-way up the rear wall of the cabinet and thence extending at an angle across th upper portion of the side walls. The re maining nine tubes extend up the rear wall of the cabinet and are spread out and extend over the top wall as shown in Figs. 1 and 2. All of the tubes are fastened to the rear wall by the clamping strip 56 and all are extended to the top wall by the clamping strip 58.

The header 50 may be clamped directly to the rear wall of the primary evaporator 26, but I prefer an alternative arrangement whereby an additional tube 60 extends upwardly out of one end of the header 50 and thence laterally at a slight angle. This tube 60 is flattened as shown in Fig. 3 and is clamped by the clamping strip 82 and screws 64 to the rear wall of the primary evaporator 26. The header 50 is partially filled with a volatile liquid 66 such as very pure anhydrous ammonia. The ammonia vapor will flow from the upper portion of the header 50 and condense upon the walls of the tubing 60 which is cooled by the primary evaporator, and this condensed liquid will thence return by gravity to the header 50 by reason of the slope provided for the tubing 60,

In the event that the secondary heat transfer circuit cools the food compartment below the temperature desired. an inert gas such as nitro gen may be introduced therein. This inert gas will collect in the tubing 60 and will block of! more or less of the upper end thereof as the load is light or heavy.

According to the present invention, I employ in the tube 68 a plurality of strands 12 of glass wool slivers, preferably arranged in the propor- 5 tions shown in Fig. 4. This glass wool silver is formed of discontinuous glass fibers having a nominal diameter 01' two microns or .00008". Within a tube, for example, I arrange the strands so that there will be 40 strands at the bottom and increasing this number of strands by steps until the upper portion of the tubing contains about 70 strands. It should be understood that the 40 strands extend the entire length of the tubing, while 10 additional strands extend about the upper three-fourths 'of the length of the tubing. a second group of 10 additional strands extend about one-half the upper length of the tubing, while a third group of 10 additional strands extends about the upper one-fourth of the tubing,

For convenience in handling, all the strands are encased and compacted in a braided sleeve ll of glass thread. The assembly of strands and the braided sleeve Ill is in turnenclosed in a braided casing ll of wire having its wires rather widely spaced so as to resemble a screen. The braided casing 18 spaces the glass fiber capillary material from the walls of the tubing forming an annular space in direct thermal communication with the surface of the capillary material and serves as a heat conductor. The braided casing '|l enclosing the strands is drawn into the tubing before the tubing is connected to the header and closed at its upper end. Each of the tubes and its wick extends nearly to the bottom of the header 50, so that the bottom of the glass wool strands are kept continuously saturated with the anhydrous ammonia liquid. The strands are packed very tightly into the tubing to a progressivelyincreasing density f ab t; 2

to .5 g./cc., from bottom to top, so that a desirable size of capillary space is provided between the glass wool fibers, Whenever convenient, it is possible to omit the braided sleeve I to apply the braided casing 18 tightly around the strands.

In Fig. 5 I have shown a modification in which the tube 82' is provided with a capillary structure in which some of the strands 84 are formed from continuous glass fibers having an average dimeter of .00022", and other strands 86 are formed of finer discontinuous glass fibers having an average diameter of .00008". 'These strands are preferably enclosed in a braided casing 88 of either the continuous or the staple type of fine glass fiber which,.in turn, is enclosed by a braided casing 90 of wire which is held tightly within the tube 82. In this form the discontinuous strands O of fine fiber makes it possible to raise the liquid to high levels, while the strands 84 of coarser continuous filament fiber makes it possible to get adequate fiow of liquid.

In the form shown in Fig. 6, the strands 92 are all of the fine discontinuous type enclosed in a casing of braided continuous glass fiber 94 which in turn is enclosed in a braided casing 96 of wire.

In this form, however, the tubing 98 is tapered so that the fibers are compressed more at the upper end than at the lower end so as to obtain a high liquid lift. This arrangement provides progressively increasing density and capillarity from bottom to top within the limits of .2 to .5

s./cc.

In all of the forms the liquid ascends through the capillary spaces between the fibers up through the tubing and saturates the fibers in the tubing. The heat within the food. storage compartment passes through the walls 28 of the inner liner to the walls of the tubing. This heat then passes through the walls of the tubing and thence capillary material.

directly to the liquid held by the-outermost fibers of the wick. This liquid on the outermost fibers adjacent the .wire braiding freely evaporates and the vapor passes down through the annular space formed by the wire braiding to the header II. from which point it ascends into the tubing II where it condenses and returns. to the header II. The wire braiding 18 makes it possible-to evaporate the liquid refrigerant at the surface of the capillary material without restriction. The wire braiding 18 serves as a heat conductor between the walls of the tubing and the surface of the It also provides a space directly adjacent the surface of the capillary material for receiving the evaporated refrigerant directly at the point of evaporation. This space provided by thewire braiding I! also conducts the evaporated liquid to the header 0 for condensation. This makes it possible to improve the .efllciency of the capillary heat transfer arrangement. Where it is unnecessary to transfer heat for more than a short distance, compacted metal wool fibers may be used as the fibrous material.

. While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. A secondary heat transfer device wherein a volatile liquid evaporates ata temperature equal to or greater than the temperature at which it condenses, comprising sealed container means having two points exposed to two different temperatures, said container means containing capillary means in the form of packed fibrous material extending continuously from one of said points to the other, one of said means .being provided with a passage connecting said points, said container means containing a volatile liquid in contact with said capillary means said container means being smaller in the upper portion than in the lower to more tightly pack the fibrous material in the upper portion.

2. A secondary-heat transfer device wherein a volatile liquid evaporates at a temperatur equal to or greater than the temperature at which it condenses, comprising sealed container means having two points exposed to two diiierent temperatures, said container means containing capillary means in the form of packed fibrous material extending continuously from one of said points to the other, one of said means being provided with a passage connecting said points, said container means containing a volatile liquid in contact with said capillary means, said fibrous material being enclosed within a wire structure in heat exchange relation with said two points.

3. A secondary heat transfer device wherein a volatile liquid evaporates at a temperature equal to or greater than the temperature at which it condenses, comprising sealed container means having two points exposed to two different temperatures, said container means containing capillary means in the form of packed fibrous material extending continuously from one of said points to the other, one of said means being provided with a passage connecting said points. said container means containing a volatile liquid in contact with said capillary means, the fibers in said fibrous material extending generally in the same direction as the fibrous material, said fibrous material being greater in quantity in the upper por tion than in the lower portion.

' '4. A secondary heat transfer device wherein a volatile liquid evaporates at a temperature equal to or greater than the temperature at which it condenses, comprising sealed container means having two points exposed to two diflerent temperatures, said container means containing capillary means in the form of packed fibrous material extending continuously from one of said points to the other, one of said means being provided with a passage connecting said points, said container means containing a volatile liquid in contact with said capillary means, the fibrous material being packed more tightly adjacent the point of higher temperature than. the point of lower temperature.

5. A heat transfer device comprising sealed container means having two points exposed to two different temperatures, said container means containing capillary means extending from one of said points to another, said container means containing a volatile liquid in contact with said capcontaining a volatile liquid in contact with said capillary means, said capillary means being inthe form of slivers of fibrous material formed into a large number of strands, tightly packed together, and a plaited wire structure intervening between the capillary means and thecontainer means extending between said two points providing thermal conduction between the adjacent walls of the container means and the adjacent surface of the capillary means and providing passages between said two points.

7. A heat transfer device comprising sealed container means having two points exposed to two different temperatures, said container means containing capillary means extending from one of said points to the other, a volatile liquid in said container means in contact with said capillary means, said capillary means being in the form of packed slivers of fibrous material, a plaited wire structure extending around said fibrous material and being in thermal contact with the walls of said container,

8. A secondary heat transfer device including a closed metal tubular structure having two points exposed to two different temperatures, a wick extending within said tubular structure between said two points, a metal spacing structure enclosing said wick and forming an intervening spacin means contacting the surface of the wick and the interior surface of the tubular structure, said tubular structure containing a volatile liquid sufficient in amount to completely saturate the wick and provide a surplus suificient to keep the wick saturated, said metal spacing structure being constructed to provide pathways for vapor located between the surface of the wick and the interior surface of the tubular structure extending between said points.

9. A secondary heat transfer device including a closed metal tubular structure having two points exposed to two different temperatures, a wick extending within said tubular structure between said two points, a metal spacing structure enclosing said wick and forming an intervening spacing means contacting the surface of the wick and the interior surface of the tubular structure. said tubular structure containing a volatile liquid suiilcient in amount to completely saturate the wick and provide a surplus sufficient to keep the wick saturated, said metal spacing structure being constructed to provide pathways for vapor located between the surface of the wick and the interior surface of the tubular structure extending between said points, said wick being formed of very fine glass wool tightly compacted within the tubular structure.-

10. A heat transfer device including a liner member, a refrigerating system including a primary evaporator located below the liner member, a secondary heat transfer device including a header and a plurality of tubes extending out of said header into heat exchange relationship with portions of said liner, said tubes containing capillary means extending from said header into the portions in contact with the liner, said tubes including a passage connecting the header with said portions in contact with the liner, said header containing a sufllcient amount of a volatile liquid to contact and wet the capillary means. and a. conduit means extending from said header at a point above the level of the volatile liquid and extending above the level of the volatile liquid into heat exchange relation with said primary evaporator for condensing vapor discharged from said tubes into the header.

11. A heat transfer device including container means containing capillary means in the form of staple glass fibers in silver form, a wire structure tightly enclosing a portion of said capillary means, said capillary means and wire structure extending continuously from one point to another within said container means, said wire structure having a portion in contact with the container means, said container means containing a volatile liquid in contact with the capillary means.

RICHARD S. GAUGLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Gaugler June 6, i944 

